Patent Literature 1 discloses a technique for a multi-core optical connector in which a pin insert (equivalent to a plug) having a ferrule holding a fiber bent at 90 degrees is fitted into a socket insert (equivalent to a receptacle) having a ferrule holding a fiber parallel to a back plane. According to the technique in Patent Literature 1, in the mating condition, a front surface (locating surface) of the ferrule provided in the pin insert abuts on the bottom (datum surface) of an accepting section of the socket insert, thereby determining a position of the pin insert relative to the socket insert. At this time, the optical axis of a lens on a side surface of the ferrule in the pin insert and the optical axis of a lens on a front surface of the ferrule in the socket insert are aligned with each other, allowing optical connection to be carried out.